In JP-A-2006-160104, there is disclosed a hybrid vehicle having a configuration where a transmission and a motor are always coupled to a front wheel axle, an engine is coupled via a clutch to the front wheel axle, and another electric motor is always coupled to a rear wheel axle. According to this hybrid vehicle, when the vehicle is stopped, the hybrid vehicle normally performs idling stop and then starts moving when accelerator pedal operation is performed by the driver, but because engine running efficiency when the hybrid vehicle starts moving is low, the hybrid vehicle starts moving by drive force supplied from the motor as long as it is not suddenly accelerated and continues traveling by the motor until a predetermined velocity or a predetermined required drive force is reached. At this time, friction loss occurs when the stopped engine ends up being rotated by the motor, so the hybrid vehicle performs control that disengages the clutch, thereafter initiates startup of the engine when a predetermined velocity or a predetermined required drive force is reached, engages the clutch, and switches to travel resulting from drive force supplied from the engine.
Moreover, this hybrid vehicle is characterized by the following control. First, the hybrid vehicle calculates from road surface conditions a maximum torque amount that the rear wheels directly coupled to the motor are capable of transmitting, and, when an acceleration required value of the driver is larger than this transmittable maximum torque amount, calculates a torque amount that should be generated by the front wheels, and, when this maximum torque amount is equal to or less than the maximum torque amount of the motor directly coupled to the front wheels, does not start up the engine, leaves the clutch disengaged, and generates torque from the motor of the front wheels. In contrast, when the calculated value of the torque amount that should be generated by the front wheels is equal to or greater than the maximum torque amount of the motor directly coupled to the front wheels, the hybrid vehicle generates a command to start up the engine and engage the clutch. The hybrid vehicle performs clutch engagement/disengagement judgment in this manner depending by predictive control from an anticipated road surface coefficient of friction predicted from the road surface on which the hybrid vehicle travels, so the hybrid vehicle can implement actual clutch engagement with enough time and, as a result, the hybrid vehicle can quickly supply drive force from the engine to the front wheels. That is, the principle that this publicly-known example disclosed has been one that aims to avoid a delay in clutch engagement by predicting and judging whether or not the condition is a condition where engine torque is needed from the acceleration required value of the driver and the road surface conditions.
However, the control principle described above that predicts the transmittable maximum torque determined by the road surface coefficient of friction and calculates the rear wheel motor torque, the front wheel motor torque and the front wheel engine torque cannot avoid a delay in clutch engagement when one wants to quickly transition to engine travel from motor travel using battery power because of the requirement of the battery state-of-charge (SOC), for example. Further, there is absolutely no consideration of the variable speed gear ratio of the transmission coupled between the engine and the axle of the front wheels, so there have been problems such as being unable to reduce shock at the time of clutch engagement.    Patent Document 1: JP-A-2006-160104